Acute pancreatitis is a common life-threatening disorder of the pancreas. Although there are several known etiologies, the mechanisms leading to the disease are unclear. However, we do know that irrespective of etiology an early step is the premature activation of digestive proenzymes (zymogens) within the pancreatic acinar cell. Our previous studies demonstrate that this activation requires a distinct pathologic rise in cytosolic Ca2+. However, the downstream effectors of the Ca2+ rise are not known. An important target of Ca2+ is the Ca2+/calmodulin-dependent serine/threonine phosphatase PP2B, or calcineurin. It has been associated with pancreatitis and also plays a role in pancreatic physiology. The hypothesis of this proposal is that calcineurin activation due to a rise in acinar cell Ca2+ mediates pathologic pancreatic zymogen activation. In this proposal, using a combination of pharmacologic and genetic strategies, we will (1) characterize the calcineurin isoforms expressed in the pancreatic acinar cell, (2) study the role of calcineurin in premature pancreatic zymogen activation in isolated pancreatic acinar cells, and (3) study the role of calcineurin in vivo on long term effects of pancreatitis. Our primary methods will be to use calcineurin inhibitors, CN isoform-specific knockout mice, and siRNA knockdown. In preliminary results, we have shown that (1) calcineurin A-alpha is distributed in the cytoplasm of pancreatic acinar cells and (2) calcineurin inhibition reduces premature zymogen activation without affecting acinar cell enzyme secretion. It is anticipated that these studies will provide new insight into the factors causing pancreatitis and may also suggest prophylactic treatment strategies that target calcineurin in the pancreas.